1. Field of the Invention
The present invention relates to a cognitive radio (CR) base station in a multi-user multiple-input multiple output (MIMO) CR communication system, and a communication method for the CR base station.
2. Description of the Related Art
As a number of data communication services increases, a usable frequency through which a service is readily provided is becoming saturated. A cognitive radio (CR) communication technology enables a secondary communication system, for which use of a predetermined frequency band is not allowed, to use the predetermined frequency hand under a condition that the secondary communication system does not interfere with communication being performed by a primary communication system, for which use the predetermined frequency band is allowed, is not using the corresponding frequency band.
In a CR communication environment, utilization of a degree of spatial freedom through a multi-antenna is needed so as to more effectively use a limited usable frequency, to increase a data transmission rate, and to not send interference on communication of a primary communication system.
Accordingly, a multiple-input multiple-output (MIMO)-based beamforming scheme in which a CR base station and CR terminals use multi-antennas may be considered.
However, a beamforming scheme that maximizes a minimum signal-to-interference- and noise ratio (SINR) of a CR terminal without giving interference from the CR terminal on a primary communication system, may need an optimization process that requires a complex iteration process to obtain a beamforming weight. Therefore, there is a desire for a beamforming weight vector obtaining method that has less complexity than the beamforming scheme, maximizes the minimum SINR, and increases a channel capacity of a CR system, and a power controlling method thereof.